Method of forming fiber glass pipe with integral joint thread



Feb. 17, 1970 w. H. PIERPONT, JR 7 METHOD OF FORMING FIBER GLASS PIPEWITH INTEGRAL JOINT THREAD Filed Sept. 30, 1968 3 Sheets-Sheet 1INVENTOQ A Fl G; 3 WIIIVLIAM H. P|ERPONT,JR.

. ATTOR NEYS Feb. 17, 1970 3,495,627

METHOD OF FORMING FIBER GLASS PIPE WITH INTEGRAL JOINT THREAD W. H.PlERPONT, JR

3 Shets-Sheet 2 Filed Sept. 30, 1968 .ATI'ORNEYS Feb. 17, 1970 w. H, PIERPONT, JR 3,495,627

METHOD OF FORMING FIBER GLASS PIPE WITH INTEGRAL JOINT THREAD FiledSept. 30, 1968 3 Sheets-Sheet 5 N M &. til? ID LO J I INVENTOR WILLIAMH. Pl ERPONT, JR

ATTORNEYS United States Patent 3,495,627 METHOD OF FORMING FIBER GLASSPIPE WITH INTEGRAL JOINT THREAD William H. Pierpont, Jr., Wichita,Kans., assignor to Koch Industries, Inc., Wichita, Kans, a corporationof Kansas Filed Sept. 30, 1968, Ser. No. 763,564 Int. Cl. 1332b 31/00;F161 9/00 U.S. Cl. 138109 Claims ABSTRACT OF THE DISCLOSURE Glassreinforced plastic pipe having preformed threads integrally disposedtherein formed by: (1) molding threaded portions wherein the outersurface is preferably corrugated or irregular and which tapers down tothe inside diameter of the pipe to which the thread is to be attached;(2) mounting said molded thread on the end of a mandrel; and (3) forminga pipe on said mandrel by providing pretensioned filamentousreinforcements longitudinally and helically disposed thereon andimbedded in a cured resin. The described tapered portion and corrugatedportion of the thread is overwound with the above-mentioned helical andlongitudinal filamentous material.

BACKGROUND OF THE INVENTION This invention relates to glass reinforcedresin pipe and more particularly to reinforced resin pipe havingpremolded threaded end portions integrally attached thereto.

Resin pipe reinforced with glass filamentous material is well known tothe art and possesses a number of advantages over metal pipe, e.g.,inertness, low weight, corrosive resistance, and high strength. Theseproperties make such pipes particularly suitable for use in the chemicalprocessing industry and in the oil industry for use as line pipe,downhole tubing, etc.

Threaded end portions of glass reinforced resin pipes have been formedby a number of methods. One method employed the use of discrete couplingmembers for joining threaded adjacent ends of resin or plastic pipe.However, since two threaded ends of pipe are joined by an interposedconnector, the possibility for leakage is doubled. In addition, the timeand effort necessary for assembly is increased as well as thepossibility for damage during assembly.

The use of threaded end portions is a considerable improvement over theemployment of discrete coupling members; however, the formation ofthreaded end portions simultaneously with the formation of the pipe byvirtue of a threaded nipple-like member over the end portion of therotatable mandrel is also subject to some disadvantages. For example,care must be taken to avoid the entrapment of air in the resin in theformation of the threads and to assure uniform and complete filling ofthe threads. Thus, an extra step is introduced into the formation of thepipe. The application of release agents to the threaded nipple end mustalso be carefully applied to insure a good release of the thread andfurther, to prevent any damage to the threads when the finished pipe isremoved from the mandrel.

Another method involved scribing grooves in a finished pipe to formthreads therein. However, this method is extremely tedious and resultedin a high rejection rate of the threads by virtue of broken threads andexposed fiberglass strands. If threads are improperly formed and must berejected, this cannot be discovered until the entire pipe has beenformed and removed from the mandrel.

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A novel method has now been found for forming glass reinforced resinpipe having threaded end portions which possess significant advantagesover prior art pipe and methods for forming same.

SUMMARY OF THE INVENTION The glass reinforced resin pipe of the presentinvention is composed of a cured resin and tensioned strands oflongitudinal and helical glass filaments arranged generally parallel andtransversely, respectively, to the longitudinal axis of the pipe withpreformed threaded end por tions bonded to said pipe by virtue ofoverwinding at least a portion of the outer surface of the premoldedthread which has been treated to provide good bonding to said resin andsaid filament windings.

The thread is premolded, for example, in conventional compressionmolding equipment, using an appropriate thermoset resin. The particularresin employed is not critical nor is the employment of specific fillersor reinforcing material therein. The particular composition of themolding material for the formation of the thread is selected for thespecific end use to which the pipe is to be used.

The thread, which may be either male or female, is preferablyconstructed so that the back portion tapers down to a dimensionsubstantially the same as the inside diameter of the pipe to which itwill be attached. Preferably, the outside surface of the thread or atleast a portion thereof, is irregular, i.e., corrugated, scored, ortreated by other suitable means to provide the maximum of adhesion andmechanical locking of the resin and the filament winding materialthereto.

The preferred method of treating the outer wall includes the formationof corrugations or striations in the outer wall. It should beunderstood, however, that the irregular surface may be prepared by anymethod which would provide the desired roughened exterior. For example,in addition to providing the desired surface condition during moldingthe already molded thread may be abraided or etched or granular materialmay be attached thereto by adhesive. The purpose of the irregularstructure of the outer wall of the premolded thread, however, is toprovide greater adhesion between the premolded thread and the resinsaturated glass roving.

The premolded threads are then placed at the ends of a mandrel ofconventional winding apparatus and the pipe is formed employinglongitudinal and helically wound strands of fiberglass imbedded inresin. The tapering portion of the thread structure is overwound withthe helical and longitudinal windings thus providing a threaded portionbonded in place by virtue of the cured resin and mechanically locked inplace by virtue of the glass filament windings thereon.

Thus, the novel pipe of the present invention would not be subject torejection by virtue of improperly formed threads applied thereon sincedefective threads would be rejected prior to the formation of the pipe.The selection of materials for the formation of the thread is muchbroader since the full range of compression molding materials can beemployed in preforming the thread whereas many materials could not beused for in situ formation of threads during the manufacture of thepipe. By the proper selection of the compression molding material, thethreads, therefore, can possess a harder and smoother surface than thatwhich is now obtainable in threaded reinforced glass pipe. Theemployment of preformed thread also provides for greater ease ofmanufacture of the pipe in that the removal of the pipe from the mandreldoes not require rotation of the pipe to remove the thread from theforming mold, as would be necessary with an in situ formed thread.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a fragmentary sectional viewillustrating a premolded female thread prior to the bonding of saidthread to a glass reinforced resin pipe;

FIG. 2 is a fragmentary sectional view illustrating a premolded malethread prior to the bonding of said thread to a glass reinforced resinpipe;

FIG. 3 is a fragmentary sectional view of a premolded female threadintegrally secured to a resin reinforced pipe on a mandrel in assembledrelationship;

FIG. 4 is a fragmentary sectional view of a premolded male threadintegrally secured to a resin reinforced pipe similar to the view ofFIG. 3; and

FIG. 5 is a fragmentary plan view of an apparatus employed in makingglass reinforced resin pipe.

DETAILED DESCRIPTION Referring now to the drawings, in FIG. 1 is shownfemale premolded thread construction 10, the inner walls comprisingthreaded portion 15. The outer wall of the molded thread, adjacent end13 which would abut the pipe to which it is to be attached comprises atapered portion 12 which tapers to the inside dimension of the pipe towhich it is to be bonded. Outer wall portion 11 comprises corrugationsor striations 14 Which provide maximum adhesion to the resin and theglass filaments.

FIG. 2 illustrates a male molded thread 16 wherein the forward portionof the outer wall is composed of a threaded portion 17 and the rearwardportion of wall 18 includes corrugations or striations 19. The trailingend of the outer wall 21 tapers to a dimension intermediate the wallthickness of the finished pipe of the pipe to which it is to be bonded.

The pipe with the premolded thread integrally attached thereto is formedin accordance with conventional methods, for example, in accordance withthe method disclosed in U.S. Patent No. 3,202,560, issued Aug. 24, 1965.The body of the pipe is composed of alternate layers of longitudinal andhelical glass filaments imbedded in a cured resin, preferably an epoxyresin. The resulting pipe is noted for its high tensile and burststrengths as well as corrosion resistance which, by virtue of thepresent invention, now possesses superior characteristics with respectto the threaded end portions thereof.

The premolded female threads are inserted on the end of mandrelsgenerally employed in the construction of reinforced fiberglass pipe,for example, the lathe type apparatus schematically shown in FIG. 5. Asuitable means for mounting the molded thread portions on the end of themandrel are employed including preferably an insert in the thread itselfto center the molded thread on the mandrel. The mandrel itself is thencoated with a parting layer, such as parafiin (see for example US.Patent No. 3,231,442), or some other suitable parting compound toprevent the adhesion of the resin, as it cures, to the mandrel and toprovide easy removal of the finished cured pipe from the mandrel. Thepipe is then prepared by building up to the desired thickness in themanner disclosed in US. Patent No. 3,202,560, and 3,231,442 by applyingalternate layers of longitudinally arranged and spirally wound glassroving.

The male thread is preferably inserted over the outside of a partiallyformed pipe and then overwound with sufficient additional layers offilamentous material to provide the necessary strength. Alternatively,the male thread is selected having a dimension slightly larger than thefinished pipe and the necessary overwinding is carried out only over thethread and a sufficient length of the pipe to provide the necessarystrength.

Preferably, the glass filaments are an untwisted re lationship. It isalso preferred that the glass filaments be arranged substantiallytransversely to the mandrel longitudinal axis in the spiral helices andarranged parallel to the mandrel longitudinal axis in the longitudinalassemblages. Thus, any tensile or bursting forces imparted to the pipemay be reacted to efficiently by the individual filaments of the glassreinforcement. Preferably, the initial glass filament layer applied tothe mandrel surface including the corrugated outer wall portion of themolded thread comprises a longitudinal assemblage or sock of glassroving. The glass strands of said assemblage are arranged parallel tothe longitudinal axis of the mandrel. The pipe is then built up ofalternating longitudinal and helically wound glass roving imbedded in amatrix of resin wherein the filaments are tensioned so that when thefinal thread pipe is employed, these tension forces may be utilized inresisting destructive forces which may be applied to the pipe.

The number of alternating layers of filaments is not critical but isdetermined by the operator depending upon the desired strength and theapplication of the finished pipe.

It should be understood that while the preferred arrangement of thefilaments is parallel to the longitudinal axis of the pipe, that thelongitudinal filamentary layers may be disposed at an angle to thelongitudinal axis, tag, at a 5 to 20 angle to the longitudinal axis. Instill another alternative, the layers of filaments are arranged in asingle angle to the longitudinal axis of the pipe. Preferably, the angleranges from 45 to Turning now to FIG. 5, a longitudinal strandassemblage 49 is placed under tension by means, for example, of alocking ring 47. A spiral wrap of glass roving 51 in widely spacedhelices is wound about the longitudinal assemblage 49 to provide goodcontact with the mandrel surface. Platform 44 is reciprocally movablealong the length of the adjacent rotating mandrel by means of rotatingscrew 40 which is driven by the reversible motor 42. Mounted on platform44 are two or more spools 43 of glass roving which are controlled so asnot to rotate until a predetermined torque is applied thereto. Glassroving strands 45 are fed from spools 43 and helically wound around therotating mandrel and overlying strand assemblage 49 so as to form alayer 55. Simultaneously, with the wrapping of the glass roving, resinis deposited thereon through resin dispensor 46, which serves tostaturate the glass roving. The sequential application of longitudinaland helical layers of glass roving is continued until a predeterminedwall thickness of the pipe is achieved. At this point, the premoldedmale thread is fitted over the end into place. Then additional layers offilamentary material is applied to obtain the desired wall thickness andsecure the thread to the pipe.

FIGS. 3 and 4 illustrate the simultaneous formation of the pipe with theintegration of the premolded thread thereon. In FIG. 3, premolded femalethread 10 is mounted on the end of mandrel 30 and centered in positionby insert 31 which releasably engages the threads 15. Theabove-described pipe formation process provides alternating layers oflongitudinal glass roving 25, 26 and 27 with helically wound strands 33,34, and 35. The corrugations 14 in outer wall 11 provide receptacles forthe applied strands of glass roving and resin which grips the threadedstructure thus providing the maximum strength, bonding the premoldedthread to the thus-formed pipe. Insert 31 may comprise any suitablematerial, e.g., metal, wood, or plastic. Any means may be employed toremove the inserts after the manufacture of the pipe, e.g., dissolving,smashing, etc. In a particularly preferred embodiment, the inserts arecomposed of foamed plastic.

In FIG. 4, the molded male thread of FIG. 2 is shown in integralrelationship to the pipe. Molded thread 16 is inserted onto thepartially formed pipe on mandrel 30 wherein the pipe is only composed offilamentary layers 25, 26, 33, and 34. The application of the remainingfilaments and resin is then continued to secure the thread to the pipe.

After the application of the alternate layers of the longitudinal andhelical glass roving imbedded in cured resin is complete, the resin isthen cured by appropriate means; i.e., a self curing resin may beemployed or external curing conditions are applied to the pipe such asheat or application of a curing agent. The pipe is then removed from themandrel. Any remainingparting compound adhereing to the interior of thepipe is then removed.

The composition employed in forming the premolded threadsis notcritical. Any suitable thermoset resin can be employed and, as statedabove, the particular composition which will produce the desiredhardness, corrosion resistance, tensile, etc., can be preselecteddepending upon the particular end use of the pipe into which it is to beincorporated. It is particularly preferred that the molding compositioncontain a filler. Particularly preferred is the incorporation ofrelatively short glass fibers or fibers of a suitable synthetic resininto the molding composition to provide enhanced strength to the moldedthread structure.

Epoxy resins are preferred for saturating the filaments of the presentinvention and for molding the threads. The term epoxy resin, as usedherein, denotes the resinous reaction product of certain epoxidecompounds and compounds having available hydrogen atoms linked to carbonatoms by oxygen atoms, as, for example, polyhydric phenols andpolyhydric alcohols. A particularly useful epoxy resin is the reactionproduct of an epihalohydrin and a polyhydric phenol, as exemplified bybisphenol-epichlorohydrin. Suitable epoxy resins include the reactionproducts of epihalohydrins and a polyhydric alcohol such as ethyleneglycol, propylene glycol, trimethylene glycol and the like. Otherequivalent epoxy resins are well known to those skilled in the plasticsart.

Other suitable resins include polyester resins, and, in particular, thealkyd resins comprising the reaction product or copolymers of polyhydricalcohols and dibasic acids. Typical of the large number of availablepolyester resins are the copolymers of phthalic anhydride and apolyhydric alcohol such as ethylene glycol, diethylene glycol orglycerine, maleic anhydride and a polyhydric alcohol, sebacic acid and apolyhydric alcohol, and diethylene glycol and bis-allyl carbonate. Theseand equivalent polyester resins are advantageously partially polymerizedprior to their incorporation in the plastics composition, and may bemodified in the manner known in the art by the admixture therewith ofsuch modifiers as epoxidized oils and unsaturated fatty acids. Ifdesired, suitable polyester polymerization catalysts well known to theart may also be included in composition.

Other polymers that can be employed include the acrylic compounds, andthe phenol formaldehyde, furfural formaldehyde, andresorcinol-formaldehyde resins. Moreover, the saturating material neednot be in every case what is commonly and rather loosely known as aresin. For example, substances such as phthalic anhydride and diallylphthalate may be employed as a thermosetting reactive material in theplastic composition.

The method employed in forming the pre-molded threads is conventional.Molding material is placed in a mold corresponding to the desired maleor female thread desired and heat and pressure are applied to effect theformation of the premolded thread and to cure the resin moldingcomposition.

What is claimed is:

1. A glass reinforced resin pipe comprising cured resin and tensionedstrands of glass filaments imbedded in said cured resin; said pipehaving a premolded thermoset resin thread portion bonded thereto andoverwound with said glass filaments at least a portion of the outer wallof said premolded thread portion having irregularities therein and saidmolded thread portion containing a rear tapering outer wall portion saidtaper being in the direction of the center of the pipe.

2. The product of claim 1 wherein said glass filaments are composed oflongitudinal and helical filaments arranged substantially parallel andtransversely, respectively, to the longitudinal axis of said pipes.

3. The product of claim 1 wherein said resin is epoxy resln.

4. The product as defined in claim 1 wherein said glass filaments areuntwisted.

5 The product as defined in claim 1 wherein said pipe contains aninternally threaded coupling end and an opposed externally threadedcoupling.

References Cited UNITED STATES PATENTS 2,876,154 3/1959 Usab 138100 X3,073,475 1/1963 Fingerhut 220-3 3,381,715 5/1968 Michael l381093,381,716 5/1968 Michael 138-109 HERBERT F. ROSS, Primary Examiner US.Cl. X.R.

